Shaping is a material modification process that often involves the application of chemical processes and/or mechanical forces to materials, particularly brittle materials, such as glass, sapphire, or silicon. Other common examples of materials that are often processed to create products via shaping include, but are not limited to, amorphous solid materials, crystalline materials, semiconducting materials, crystalline ceramics, polymers, and resins.
Typical techniques for shaping brittle materials include mechanical saw processes, scribe and break, direct laser machining, laser thermal shock cleaving, mechanical grinding, mechanical polishing, abrasive liquid erosion, flow honing, chemical etching, or a combination of mechanical, laser, liquid and chemical steps. Although the net results of these techniques are somewhat different from one another, they all share the drawback of insufficient control of the as-shaped surface or bulk properties.
Brittle materials are used in multiple commercial markets for consumer, industrial and medical goods. There are aspects to be taken into consideration when processing and manufacturing products with brittle materials.
In the aspect of a material cutting/processing speed, multiple figures of merit (FOM) are used in commercial markets for quantifying the effective brittle materials shaping speed. For example, the linear cutting speed can be calculated by dividing the total length of material cut by the total cutting time, which generates an effective cutting speed with measurement units in meters per second (m/s). Depending on the exact material species, material thickness and desired surface characteristics, the effective cutting speed can also be in the units of millimeters per second (mm/s).
Takt time, cycle time, is another example of an FOM for quantifying the effective shaping speed for brittle materials, which is the time required to produce a unit of the shaped portion of brittle material from an initial substrate of brittle material. The Takt time for a production line is often characterized by number of seconds, or minutes, required to produce a unit. The Takt time calculation can include the linear cutting speed as a variable. The Takt time can also include additional steps required to produce the finished unit as variables in the calculation, such as grinding, polishing, etching, annealing, chemical bath, or ion-exchange treatment.
In the material property aspect, brittle materials can be characterized by the lack of plastic deformation prior to breaking when a stress is applied to the material. When subjected to stress, a brittle material breaks without significant deformation (strain). This property is not exclusive of strength, since some brittle materials can be very strong, such as diamond, sapphire or strengthened glass.
In the manufacturing aspect, brittle materials can be especially challenging to shape (e.g., cut, drill or mill), with controlled surface properties since these materials tend to chip and/or crack using typical methods. These defects are usually the result of “brittle fracture,” which are cracks that propagate through a stressed material along paths of least resistance. The intrinsic microscopic stress anisotropy of brittle materials, and/or the randomized local stress applied by traditional shaping tools, imposes uncontrolled surface shape and/or surface morphology on the as-shaped edge. This uncontrolled edge quality can result from cracks running along transgranular pathways in the brittle material tracing the lattice orientation within each microscopic grain element in the material. Similarly, the uncontrolled edge quality can result from cracks running along intergranular pathways in the brittle material traversing the grain boundaries between individual grain elements in the material. The limitations of controlling the as-cut edge quality of a brittle material with traditional techniques are depending upon the grain size in the material and/or the dislocation mobility allowed by the grain structure.
Typical methods of shaping brittle materials fail to control the as-shaped surface shape and/or surface morphology since they apply a force (such as mechanical and/or thermal) that often leads to crack propagation along native crystallographic planes of high shear stress of the brittle material. Defects within the bulk of the brittle material substrate can be the result of the crystal growth process, impurities, or the stochastic grain pattern. Similarly, defects at the surface of the brittle material substrate can result from the crystal growth process, impurities, the stochastic grain pattern, or the substrate forming process, e.g., melting, drawing, fusing, slicing, lapping or machining. The uncontrolled crack propagation common with the typical methods can be caused by the shaping tool. Mechanical shaping tools can have microscopically random shapes, hardnesses, and/or applied forces. Thermal shaping tools can create microscopically random heat distributions in the brittle material.
FIG. 1A illustrates a typical method 100 of cutting a stock of brittle material 101 (hereinafter “material” 101) using a typical tool 102 such as a mechanical diamond-tipped saw. When the typical tool 102 is applied on the material 101, a cutting/breaking/cracking line 104 is created. A first portion 106 and a second portion 108 are formed by separating the material 101 into two or more pieces. The material 101, such as a brittle material, forms rough surfaces 110 when the typical tool 102 is applied to cut the material 101.
FIG. 1B illustrates three rough surfaces 112, 114, and 116 made by using typical methods and devices for cutting a brittle material. The rough surfaces 112, 114, and 116 have respectively large, medium and small roughness profiles of the brittle material 101 created by application of the typical tool 102. When the size (length in any directions) of the defect 118 is greater than a size of a critical defect, such as equal to or greater than 10˜20 microns, the brittle material 101 can crack or become easy to break at a predetermined amount of impact of force.
Although the typical methods of and devices for brittle materials surface shaping have allowed shaping into predetermined shapes, these typical methods and devices impose uncontrollable surface properties in the resultant surface as shown in FIG. 1B. Multiple process fabrication protocols are therefore required in the typical process and methods, whereby the shaped surface is subsequently conditioned to achieve the desired surface properties, which are time consuming and associated with higher manufacturing costs. For example, an electronic display panel comprising thin glass typically exhibits micro-cracks and chips of uncontrolled dimensions along the shaped surface(s), and these features are typically removed via multiple steps of fine grit polishing of the surface(s) in the typical methods. Polishing, grinding, lapping, etching, sanding, annealing, and/or chemical bath are part of the subsequent steps for after-shaped edge treatment process in the typical methods.